Question

The vapour pressure of pure water is $32.8mm$ of $Hg$. It is mixed with ethanol which has mole fraction $0.9$.

Find the vapour pressure of the resulting solution:

• A. $39.3mm$ $Hg$
• B. $36.0mm$$Hg$
• C. $29.5mm$ $Hg$
• D. $28.8mm$ $Hg$

Answer 1

The correct option is C $29.5mm$ $Hg$

The reduction of the vapour pressure of the solvent is given as follows:

$p_1=x.{p_1}^0$

Here, $p_1$ is the vapour pressure of the solution.

${p_1}^0$ is the vapor pressure of pure solvent.

$x$ is the mole fraction of solute.

Vapor pressure of pure water is ${p_1}^0=32.8$ mm of Hg

Mole fraction of ethanol $=x=0.9$

Vapor pressure of solution is $0.9\times 32.8=29.52$ mm of Hg